Early circuit board fabrication techniques involved connecting wires on the surface of the circuit board directly to through holes. Through holes, when plated with a conductive material, serve to connect the front and back surfaces of the circuit board. Unfortunately connecting wires directly to the through holes produced connections that had a high failure rate. The difference between the thermal expansion of the metal wire and the substrate lead to cracking, particularly at the juncture of the wire and the through hole. As a result, the electrical connection between the wire and the through hole was broken.
To overcome the failure rate of the connections, a land was created to connect the wire to a through hole. The land which is made of electrically conductive material, typically copper, is a circular or more specifically annular structure, that completely encircled the through hole. By providing lands the surface area of the connection between the through hole and the wire was significantly increased; this resulted in fewer failed connections.
Lands have been historically annular, to maximize the contact area between the edge of the plated through holes and the land. In addition, lands were circular in configuration to compensate for errors in drilling or photolithography that caused the lands to be offset from the through hole during the printed circuit board fabrication process.
In the quest for miniaturization of circuit boards and integrated circuit devices, designers have sought to place more and more electronic structures on the surface of circuit boards and devices. To accomplish this goal, designers require an ever increasing amount of space, that is "real estate," on the surface of a circuit board. In an attempt to increase the available "real estate", the diameter of conventional lands relative to the diameter of through holes was decreased. However, when the through holes were drilled, the drill bit often stripped the lands from the substrate, leaving an irregularity in the through hole which creates an unreliable plated through hole.
Indeed, as circuit board technology has developed, the land size has increased rather than decreased. Projections known as "flares" have been added to lands along the axis of the wire to further improve the reliability of the connection between the wire and the land. The addition of the flares to circular lands consumes even more real estate than the conventional lands.
It would be desirable to increase the available real estate on a substrate while preserving reliable connections between wires and through holes afforded by lands.